Collocations for skull - noun

human
thick, thin
fractured
He suffered a fractured skull in an accident in April.

grinning
the angel of death with his grinning skull

crack, fracture
crush, shatter, smash

fracture

a fracture of the skull, a fracture to the skull (BrE)
suffer a fractured skull (esp. BrE)
He suffered a fractured skull in an accident in April.

skull and crossbones
The ship was flying a pirate flag with the skull and crossbones on it.